This invention relates to smelting.
Smelting is an important process used for the production of many metals and alloys. Smelting takes place in a furnace with the heat necessary to melt the contents of the furnace being produced electrically. A DC arc plasma furnace is an example of a smelting furnace in which pre-baked graphite electrodes are conventionally used to direct electrical energy into the furnace bath. The consumption of the electrodes is an important cost item in the use of such a furnace.
Sxc3x6derberg electrodes are used in various smelting processes. The Sxc3x6derberg electrode comprises a casing which may have a plurality of inwardly projecting ribs. Electrode paste, which typically comprises a mixture of a carbonaceous material and a hydrocarbon binder, is introduced into one end of the casing. The paste passes down the casing until a zone is reached where it is subjected to a suitable calcining temperature to expel volatile substances and bake the paste into a hard form. The hard form emerges from an end of the casing and forms the working end of the electrode.
The present invention provides the use of a pre-baked graphite or similar electrode in combination with a Sxc3x6derberg electrode.
Thus, according to a first aspect of the invention, an electrode for a smelting furnace comprises:
an elongate casing including a plurality of spaced, inwardly projecting ribs extending radially from an inner surface of the casing towards the centre of the casing;
a central core of a pre-baked electrode disposed within the casing free of the projecting ribs and defining a space between the core and the inner surface of the casing;
a heating zone located intermediate the ends of the casing; and
a carbonaceous electrode paste received or receivable within the space between the core and the inner surface of the casing, the paste being arranged to be calcined into a baked, hard form upon entering the heating zone.
The central core may either be a solid pre-baked graphite electrode or a hollow pre-baked graphite electrode defining a feed passage between open ends thereof for feeding charge material into the furnace.
The ribs are typically in the form of planar fins formed from an electrically conductive material, in particular mild steel or stainless steel. They preferably include a plurality of transversely formed apertures or holes for allowing electrode paste to pass through them so as to anchor or support the electrode upon baking.
The combined electrode of the invention will generally be cylindrical in shape and may be made of larger diameter than conventional pre-baked graphite electrodes. This enables the use of larger electrode currents and increased operating capacity. Further, the consumption of expensive graphite electrodes is reduced.
The invention has particular application to AC or DC arc plasma furnaces or Sxc3x6derberg submerged arc furnaces and in the smelting applications where pre-baked graphite electrodes have traditionally been used.